The Alaska Crab Institute defines "Snow Crab" as any of the three crustacean species: chionocetes opilio, chionoctes bairdi, or chionocetes tanneri. The latter species is also known as tanner crab. To prevent risk of toxin build-up, snow crab are required to be butchered (cleaned) when live. The butchering involves removing the carapace (back), mandible, and tail, cleaning the guts from the body cavity, and then removing the gills, thereby leaving the legs, claws and an intermediate connecting body portion. When this body portion of the cleaned crab is bisected the two crab halves are known as "sections". A "section" consists of a cleaned body portion (often referred to as the "shoulder") connected by joints to a set of legs consisting of four walking legs and a non-walking leg supporting a claw. For purposes of this discussion, the "length" of a crab has reference to the mandible to tail dimension, and the "width" has reference to carapace dimension in the direction of the two sets of legs of the crab.
After the crab has been cleaned and sectioned, the sections are normally cooked, frozen and bulk-packed in fiber-board containers. It is preferred to accurately split the cleaned crab into sections having equal body portions because such sections normally bring a larger price in the crab section market.
Machines have been devised to assist in butchering snow crabs and halving them into sections. One such machine has consisted of an endless conveyor with crab gripping carriers at regular intervals for conveying live crabs in a head first direction through processing stations whereat the crabs are automatically decarapaced, cleaned, degilled, and sectioned. Each gripping carrier has comprised a pair of laterally spaced clamping arms which are arranged to clamp the two sets of legs of a crab against a mounting plate at clamping positions leaving the carapace free to be removed therebetween. The crabs are loaded into the gripping carriers at the leading edge thereof. The clamping arms automatically open (swing-up) at an upper loading station adjacent the tail end of the conveyor whereat a crab is loaded beneath the clamping arms which then automatically close into clamping position. A star wheel, located at the head end of the conveyor engages and removes the mandible, carapace and attached tail. Sets of water jets then clean the gut and then the gills from the conveyed crab as it moves upside down in the return bottom run of the conveyor toward the loading end (tail end) of the conveyor. Next a rotary cutter at a fixed central position beneath the conveyor splits the cleaned crab into sections. The sections are then released when the clamping arms are reopened by a cam preliminary to returning to the loading station.
The described machine, although having advantages over the prior art did not operate consistently on varying sizes of crabs, particularly in the removal of carapace, mandible and tail. Furthermore, since it is unlikely that the live crabs will be perfectly centered when loaded between the pairs of clamping arms on the gripping carriers, the described prior art machine has the shortcoming of not accurately bisecting the crabs. Also, the gripping carriers are not easy to load for high speed operation of the machine and did not adapt to varying crab sizes.